1. Weak Acid-Strong Base Titration Lab
Sam White
Pd. 2

2. Titration
Titrations are a neutralization reaction between a base and an acid
The 2 types of titrations you need for this lab are:
Strong Acid-Strong Base
Weak Acid-Strong Base

3. Strong Acid-Strong Base
In a proper Strong Acid-Strong Base titration, the H+ and OH- are used up to create water in the following reaction:
H+ + OH H2O
The ions attached to the H+ ion (like Cl-) and to the OH- ion (like Na+) form a soluble salt (like NaCl) which splits into ions in water. These become spectator ions in the reaction, and do not affect the pH
When done properly, this type of titration creates a solution with a pH of 7, since the H+ and OH- concentrations are equal, and water is neutral.

4. Strong Acid-Strong Base Titration Curve

5. Weak Acid-Strong Base
Weak Acid-Strong Base reactions follow this reaction:
HA + OH H2O + A-
While the acid is fully neutralized (all H+ ions are used up to make water), the conjugate base of the acid (denoted generically as A-) remains.
This means your titrated solution will have a pH above 7 (usually somewhere between 8-9)

6. Weak Acid-Strong Base Titration Curve

7. Diprotic Acids
So far we’ve only seen examples of monoprotic acids (acids with one H+ ion)
Weak diprotic acids (acids with two H+ ions) behave a little differently:
H2A + OH H2O + HA-
HA- + OH H2O + A-2
As you can see, weak diprotic acids must dissociate twice, resulting in unique titration curves

8. Weak Diprotic Acid Titration Curve

9. Purpose
To determine the concentration of a sample of an unknown weak acid through titration with NaOH

10. Materials 50 mL Buret Ring Stand Buret Clamp .1 M NaOH
Ehrlenmeyer Flask
Graduated Cylinder
Acetic Acid
Phenolphthalein

11. Procedures: Step 1
Set up titration aparatus as shown, with 50 mL of NaOH in the buret
Buret Clamp
Buret
Ring Stand
Ehrlenmeyer Flask

12. Procedures: Step 2
Measure out 25 mL of acetic acid. Add to Ehrlenmeyer Flask.
Acid
25 mL Acid
From Clipart
From Clipart

13. Procedures: Step 3
Add 3 drops of Phenolphthalein indicator to the flask of acid.
Acid
Made From Clipart

14. Procedures: Step 4
Slowly add drops of NaOH from the buret to the flask of acid. Make sure to stop when it is a light pink color.
Before
Stop Here
Way too Far

15. Procedures: Step 5
Record the amount of NaOH needed to neutralize the acid.

16. Sample Data Trial 1 Trial 2 Trial 3 Amount of Acid 25 mL 25 mL 25 mL
Amount of NaOH
Molarity of Acid
25 mL mL mL
14 mL mL mL
? ? ?

17. Calculations
Moles of NaOH:
0.1 M = moles NaOH
Liters solution

18. Calculations Each trial NaOH:
0.1 M = moles NaOH moles of NaOH = .014 x .1 = .0014
.014 L
0.1 M = moles NaOH moles of NaOH = .017 x .1 = .0017
.017 L
0.1M = moles NaOH moles of NaOH = .015 x .1 = .0015
.015 L

19. Calculations Average moles of NaOH: 0.0014 + 0.0017 + 0.0015 = 0.0046

20. Calculations
This means, on average, moles of NaOH were used in neutralization. This means, on average, there were moles of H+ neutralized. This also means, on average, moles of Acetic acid were used.

21. Calculations Average molarity of Acetic Acid:
M = moles M =
0.025 L
This means the concentration of the acetic acid solution was M

22. Bibliography For 3 images on Procedure 4: